The present invention relates to a shaped article which is capable of resisting impact, including high velocity impact and other high energy impact.
A number of impact challenges, such as attacks with projectiles, shells, grenades, missiles and bombs, have as their main purpose to penetrate and/or damage the objects which they are aimed at. Another class of potentially damaging impact is accidental events such as gas explosions, vehicle (ships, aeroplanes, cars, etc.) collision, impact occurring during earthquakes, and the accidental dropping of articles, e.g. in the offshore industry.
Another type of impact is impact processing, such as impact hammering, explosion shaping, etc. Another type of impact occurs in connection with quarrying of stone. For example, large pieces of stone may fall onto trucks or other machinery, and high energy impacts of this type can cause extensive damage.
Impact challenges also occur in the form of high energy impact from e.g. explosives. For example, bank vaults must be able to withstand an explosive impact of this type.
In high velocity or high energy impact, the behaviour of materials is in many ways fundamentally different from the behaviour under slow static influencesxe2x80x94often resulting, inter alia, in fatal failure or destruction of the articles in question, even where the articles have very high load bearing capacity under static conditions.
For protection against damaging impact and for tools used for impacting processing, articles having better resistance against impact than hitherto obtainable are desired.
The present invention provides such articles. The articles of the invention can be designed to provide protection or resistance under influences where known art materials would fail or would be vastly inferior, in particular high energy impact such as high velocity impact.
It is known to produce various high-strength composite materials, for example construction materials based e.g. on a matrix of Portland cement and very small particles such as ultrafine silica, and with reinforcement incorporated therein in the form of e.g. fibres, steel bars or wires, etc.
EP 010777 discloses very strong and dense composite cement-based composite materials prepared from Portland cement, inorganic solid silica dust particles, fibres, a concrete superplasticizer and water, the composite materials having a large content of silica dust particles and superplasticizer and a small water content, e.g. typically 10-30% by volume of silica dust particles based on the volume of the cement and silica dust, 1-4% by weight of superplasticizer dry matter based on the weight of the cement and silica dust, and a water/powder weight ratio of 0.12-0.30 based on the weight of the cement, silica dust and possible other fine powder present.
EP 042935 discloses improved composite materials based on the matrix of EP 010777 and additionally containing a strong aggregate with a strength exceeding that of ordinary sand or stone used as aggregate for ordinary concrete.
WO 87/07597 discloses a compact reinforced composite (CRC) material based on a combination of a rigid, dense and strong matrix comprising a base matrix corresponding to the composite materials described in EP 010777 and EP 042935 which is reinforced with a high content of relatively fine fibres and which is further reinforced with a high content of main reinforcement, e.g. in the form of steel bars, wires or cables, to result in a novel composite material which is both strong and rigid as well as ductile.
A technical paper (xe2x80x9cRole of shear reinforcement in large-deflection behaviorxe2x80x9d, Kiger et al., ACI Structural Journal, November-December 1989) describes the use of xe2x80x9clacingxe2x80x9d or xe2x80x9csingle-leg stirrupsxe2x80x9d in order to tie the two principal reinforcement mats together in reinforced concrete structures designed for blast-resistance. The paper concludes that requirements for shear reinforcement such as lacing may be more restrictive and expensive than necessary, and it is stated that although transverse shear reinforcement (in the form of lacing or stirrups) can provide additional confinement for reinforced concrete beams, it provides very little, if any, additional confinement for slabs. It is furthermore suggested that the use of smaller but more numerous principal reinforcing bars may be a more effective way of preventing breakup of a concrete slab than the use of such transverse shear reinforcement. The emphasis of the paper is on the reinforcement itself, and there is no suggestion to use e.g. lacing with any particular type of concrete matrix.
Although the principle of xe2x80x9clacingxe2x80x9d of reinforcing bars in a concrete structure designed for blast-resistance, e.g. as described in the technical paper referred to above, was known, the prior art contains no suggestion to combine this or a similar principle of reinforcement together with any particular type of concrete matrix. On the contrary, the cited technical paper suggests that an increased amount of main reinforcing bars might be a more effective solution to the problem of blast-resistance than the use of transverse reinforcement such as lacing. Thus, the problem of providing structures, in particular cement-based structures, with improved blast- or impact-resistance remains unsolved.
The CRC concept described in the above-cited WO 87/07597, on the other hand, emphasises both the nature of the matrix (a rigid, dense and strong cement-based matrix) and the reinforcement (a high content of reinforcing fibres together with a high content of main reinforcement in the form of e.g. steel bars, wires or cables). However, the concept of a 3-dimensional arrangement of main reinforcement, wherein individual reinforcing elements are interlocked with each other in at least one dimension, is in no way suggested by WO 87/07597, for the simple reason that such an intricate arrangement of reinforcement would have been regarded by a person skilled in the art as involving an unnecessary expense and difficulty without any expectation of technical benefit.
It is an object of the present invention to provide novel shaped articles with improved performance characteristics, in particular under dynamic conditions. One aspect of the present invention represents a further development of the CRC concept mentioned above, enabling the production of materials that are extremely strong and durable under both static and dynamic conditions, and which also show extremely high impact resistance.
The present invention relates in general to impact-resistant articles which are based on a combination of a hard, but fracture-ductile matrix and a three-dimensional reinforcement which is internally tension interlocked in at least one dimension. Articles according to the invention are unique in showing high strength, rigidity and ductility in all three directions and showing, upon being subjected to a large load, high strength, toughness and rigidity, as well as the capability of absorbing high energy with retention of a substantial degree of internal coherence, also under exposure to high-velocity or high-energy impact.
In its broadest aspect, the invention can be characterized as a shaped article, at least one domain of which has a three-dimensionally reinforced composite structure, the composite structure comprising a matrix and a reinforcing system, the reinforcing system comprising a plurality of bodies embedded in the matrix and extending three-dimensionally in first, second and third dimensions therein, the reinforcing system being tension interlocked in at least one dimension in that reinforcement components extending in the first and/or second dimension are tension interlocked to reinforcement components extending in the same dimension(s), but at a transverse distance therefrom, by transverse reinforcement components extending in a dimension transverse to a plane or surface defined by the reinforcement in the first and/or second dimension,
the matrix having a compressive strength of at least 80 MPa, a modulus of elasticity of at least 40 GPa, and a fracture energy of at least 0.5 kN/m,
the reinforcing bodies having a tensile strength of at least 200 MPa, preferably at least 400 Mpa.
As indicated above, the present invention relates in particular to shaped articles that exhibit improved performance under dynamic conditions. Therefore, in a preferred embodiment of the shaped articles of the invention, the volume proportion of the reinforcing bodies in the reinforced composite structure is at least 2%, the volume proportion in any specific direction being at least 0.5%. Preferably, the volume proportion of the reinforcing bodies is at least 4% and the volume proportion in any specific direction is at least 0.75%, and more preferably the volume proportion of the reinforcing bodies is at least 6% and the volume proportion in any specific direction is at least 1%.
The number of reinforcing components in the reinforced composite structure domain will typically be at least 3, preferably at least 5, in any of the first, second and third dimensions of an arbitrary rectangular reference coordinate system in the reinforced 5 composite domain.
It is also preferred that the ultimate strain of the reinforcing bodies is at least 2%. However, when the reinforcing bodies have a tensile strength between 200 and 300 MPa then the ultimate strain 10 should be at least 20%, and when the reinforcing bodies have a tensile strength between 301 and 400 MPa, then the ultimate strain should be at least 15%.
The reinforcement systems in the articles according to the invention may be configured in many different ways, such as will be explained in the following, but characteristic to them all is a three-dimensional grid, network or lattice of reinforcement (which may have many different configurations as explained in the following) in which matrix material as a xe2x80x9ccontinuous phasexe2x80x9d is dispersed in the interstices of the xe2x80x9clatticexe2x80x9d, which also normally and preferably constitutes xe2x80x9ca continuous phasexe2x80x9d. Characteristic to the present invention is the fact that the reinforcement system comprises components which extend in all three dimensions, and that the concentration of reinforcement in any particular direction is above the above-stated minimum value.
It is also an essential feature of the invention that in at least one direction, the reinforcement system is internally xe2x80x9ctension interlockedxe2x80x9d, which means that at least in that direction, the reinforcement system counteracts separation in that direction. The term xe2x80x9ctension interlockedxe2x80x9d does not necessarily mean that the reinforcement in question is under tension under static conditions, but rather that when the material is exposed to tension forces that tend to separate the interlocked components of the reinforcement in question from each other, the tension interlocking provided by the transverse reinforcement components resists the separation, even under conditions of heavy destruction where matrix might fail. This is explained in greater detail in connection with the drawings.
This feature plays an essential role in the high velocity impact resistance achieved by the present invention: Take as an example (with reference to FIG. 11, which is discussed in greater detail below) a large 20 cm thick panel or plate with 20% by volume of reinforcement in the plane of the panel consisting of five layers of heavy steel bars arranged perpendicular to each other and interconnected by means of 3.1% by volume of transverse reinforcement fixing each individual steel bar in the top layer with a corresponding individual steel bar in the bottom layer. This reinforcement is embedded in and tightly fixed to a strong, stiff and fracture-ductile cement-based matrix. Such panels stopped a 47 kg armour-piercing shell (diameter 152 mm) travelling at 482 m/sec, the shell ending tightly fixed in the panels with 8 cm of its rear still extending from the front of the plate!xe2x80x94and with very little damage of the panel except in the immediate vicinity of the shell and fine map cracking of the plate surface. In the same series of experiments, plates of the same size of high quality cement-based composite and subjected to the same load were completely crushed into small pieces. In similar experiments, strong plates with matrix materials substantially identical to the above materials and strongly reinforced with reinforcement identical to the above reinforcement, but without the essential transverse reinforcement, large damage occurred. The two front plates (thickness of each plate 20 cm) were completely shattered, with materials including 20 mm steel bars 60 meters being flung backwards by the reflected wave. Such a large destruction is completely avoided with the articles of the invention.
It will be understood that the shaped article does not necessarily have the reinforced composite structure throughout the article, but that one or several domains which fulfil the criteria stated above may be present together with domains which do not conform to the criteria. As an example may be mentioned a bank vault where a domain having the defined reinforced composite structure is hidden within a wall which has a different exterior.
The reinforcing system (the xe2x80x9cmain reinforcementxe2x80x9d) will typically be made from bars, e.g. several layers of bars, with bars within a layer being arranged parallel to each other, the direction of the bars in one layer typically being perpendicular to the bars in the adjacent layer or layers. It is also possible to have layers of the reinforcement consisting of perforated plates, possibly with other layers being, e.g., bars or rods. The transverse components may be bars or rods bent around the outer layers of the main reinforcement, or other configurations, such as illustrated in the drawings. It is also possible for the transverse components to be integrated parts of one reinforcement body, e.g. where the reinforcement body consists of several perforated plates at a (transverse) distance from each other joined together with transverse rods welded to the plates in such a manner that they give a strong tension interlocking.
It should be noted that several xe2x80x9creinforcing componentsxe2x80x9d in a given dimension may be a part of a single reinforcing body. Thus, a reference herein to a number of reinforcing components in a given dimension need not be equivalent to the same number of independent (i.e. non-connected) reinforcing bodies. See e.g. FIG. 10 and the accompanying description below for an illustration of this principle.
In the preferred embodiments, the transverse reinforcement components tension interlock reinforcement components of opposite outermost planes or surfaces of the reinforcement, so that the reinforcement system as a whole resists separation in the transverse direction.
As indicated above, the reinforcing system may be tension interlocked in more than one dimension. This may be done according to the same principles described above, using e.g. rods bent around rods perpendicular thereto, or wires/cables. Another interesting possibility is to have adjacent longitudinal rods combined in a hairpin-like configuration around and enclosing the outer layers of rods perpendicular thereto. While this is not tension interlocking proper, it is an interesting further enhancement of the reinforcing system where a transverse tension interlocking is already present.
The matrix material is relatively strong, stiff and resistant to fracturing, such as appears from the above minimum criteria. Preferably, the matrix material has a compressive strength of at least 100 MPa, preferably at least 150 MPa, more preferably at least 200 MPa, more preferably at least 250 MPa and most preferably at least 300 MPa. The modulus of elasticity of the matrix material is preferably at least 60 GPa, more preferably at least 80 GPa, and still more preferably at least 100 GPa. The fracture energy of the matrix material is in particular at least 1 kN/m, preferably at least 2 kN/m, more preferably at least 5 kN/m, more preferably at least 10 kN/m, more preferably at least 20 kN/m, and more preferably at least 30 kN/m.
As appears from the above, the reinforcing bodies combined with the strong, stiff and fracture-resistant matrix are characterized by a combination of a high tensile strength and sufficiently high ultimate strain, and are present in a high volume in the matrix in any particular direction of the matrix, which means that in any cross section layer in any direction taken within the matrix domain, the volume concentration fulfils the criteria stated. It is most advantageous that the strength and strain parameters are higher than the minimum stated above. Thus, it is preferred that the reinforcing bodies have a tensile strength of at least 700 MPa, preferably at least 1000 MPa, more preferably at least 1500 MPa, more preferably at least 2000 MPa, more preferably at least 2500 MPa, and more preferably at least 3000 MPa. The ultimate strain of the reinforcing body or bodies is preferably at least 4%, more preferably at least 6%, more preferably at least 10%, more preferably at least 15%, more preferably at least 20%, and more preferably at 30%. These strong reinforcing bodies or components are preferably present in a high volume concentration in the reinforced composite structure domain, e.g. typically at least 6% by volume as mentioned above, with a genuine three-dimensionality expressed by a volume concentration of at least 1% in any specific direction of the domain. In a further preferred embodiment, the volume proportion of the reinforcing bodies in the domain which has the reinforced composite structure is at least 8%, preferably at least 10%, such as at least 15%, e.g. at least 20%, such as at least 25%, e.g. at least 30%, and the volume proportion of the reinforcing body or bodies in any specific direction of the domain is at least 2%, e.g. at least 5%, e.g. at least 10%, such as at least 15%. The volume concentration of the reinforcement should, of course, not be concentrated in a single reinforcement component. In a preferred embodiment, the number of reinforcing body components in the reinforced composite structure domain is at least 8, such as at least 15, e.g. at least 20, in any of the first, second and third dimensions of an arbitrary rectangular reference coordinate system in the reinforced composite domain.
The matrix material of the shaped articles of the invention may be prepared by methods known as such in the art; for some of the matrix materials, more detailed descriptions of their preparation are given herein. Important examples of matrices which are useful for the purpose of the invention are matrices comprising particles and fibres held together by a binder, in particular ceramics-based materials, cement-based materials, plastics-based and glass-based materials. Particularly interesting materials are metal-based materials and cement-based materials. The latter types of materials comprise the materials disclosed in the above-mentioned patent references.
For a matrix comprising matrix particles and fibres held together by a binder, e.g. a cement-based binder, the content of matrix particles and fibres in the matrix should be at least 50% by volume, e.g. at least 60% by volume, e.g. at least 70% by volume, e.g. at least 80% by volume, such as at least 85% or 90% by volume, and the content of fibres in the matrix should be at least 1% by volume, e.g. at least 2% by volume, e.g. at least 3% by volume, such as at least 5% or 10% by volume.
In a particular embodiment, when the matrix is prepared from a submatrix comprising fine particles having a size of 0.5-100 mm (e.g. cement particles), ultrafine particles having a size of from 50 xc3x85 to less than 0.5 xcexcm (e.g. microsilica particles), a dispersing agent (e.g. a concrete superplasticizer) and water, the content of fine particles and ultrafine particles in the submatrix should be at least 50% by volume, e.g. at least 60% by volume, e.g. at least 65% by volume, e.g. at least 70% by volume, such as at least 75% or 80% by volume, and the content of matrix particles and fibres in the matrix should be at least 30% by volume, e.g. at least 40% by volume, e.g. at least 50% by volume, e.g. at least 55% by volume, e.g. at least 60% by volume, e.g. at least 65% by volume, such as at least 70% or 75% by volume.
The combination of the matrix material with the main reinforcement should be performed under conditions which ensure maximum density and homogeneity of the matrix material tightly fixed to the reinforcement. Typically, the matrix material is introduced by casting in a mould in which the reinforcing system has been pre-arranged, the homogeneous distribution of the matrix material in all interstices in the reinforcement and in excellent contact with the reinforcement preferably being aided by vibration or combined vibration and pressure, such as described in the above-mentioned WO 87/07597.
Articles according to the present invention can be made in sizes from small articles such as machine parts through sizes of the order of a meter or meters length and breadth up to even very large sizes with very thick walls of more than 30 cm, such as more than 50 cm or at least 75 cm or at least one meter or even more. Such very large, thick-walled structures are suitable, e.g., for encapsulation of nuclear power stations.
Although the present description and drawings refer for the sake of simplicity to structures in which the reinforcement is found in planes which are substhantially perpendicular to each other, it will be clear that the dimensions or planes defined by the reinforcement can be at various angles in relation to each other. Similarly, reinforcement in the form of e.g. bars within a plane or layer is not necessarily aligned parallel to each other, but can be arranged as desired, as long as the basic three-dimensional reinforcing structure of the invention, including the tension interlocking transverse rearrangement, is obtained. It should also be noted that the term xe2x80x9cplanexe2x80x9d as used in the present context should be understood to also refer to e.g. a curved surface. Thus, the xe2x80x9cplanesxe2x80x9d of articles according to the invention may e.g. be the structure defined by inner and outer curves of an object with a semi-circular or other cross section which is not strictly xe2x80x9cplanarxe2x80x9d in the geometric sense of the word.
The shaped articles of the present invention are typically in the form of e.g. plates, sheets, walls or portions thereof, etc., the surfaces of which can, as indicated above, be planar or irregular, e.g. curved or angled in one or more dimensions. In such articles, the main reinforcement will typically follow substantially, i.e. more or less parallel with, the surfaces, while the transverse reinforcement typically will extend more or less perpendicular to the surfaces.